1. Field of the Invention
The present invention relates to a producing method of metal fine particles or metal oxide fine particles, metal fine particles or metal oxide fine particles, and a metal-containing paste, and a metal film or a metal oxide film. The metal fine particles and the metal oxide fine particles produced by the present invention are used for forming an electronic circuit and forming an electroconductive film in electronic materials, solder materials, forming a wire shielding layer, catalyst materials, and ceramic sintered compacts, etc.
2. Description of the Related Art
The metal fine particles and the metal oxide fine particles have high surface activity and therefore receive an attention as functional materials, and its application to various industrial fields is expected. Here, a fine particle means a particle with a particle size of about 1 nm to 1000 nm.
However, conventional metal fine particles involve a problem such as a high cost under limitation in its production process by synthesis. The metal fine particles are produced by a physical method or a chemical method.
The physical method is a method of producing the metal fine particles by heating and vaporizing metal or a metal compound in an apparatus such as a vacuum chamber and adjusting a degree of supersaturation of metal vapor. For example, patent documents 1 to 3 disclose a technique of synthesizing inorganic fine particles or metal fine particles with high purity by the physical method.
The chemical method is a technique of producing the metal fine particles by reducing metal ions or metal complex in a solution, and making a nucleus of a metal atom grow little by little. For example, patent documents 4 and 5 disclose a technique of synthesizing fine particles by using a reducing agent, with a carbonyl compound, being an organic metal compound, as a metal source. Further, patent document 6 discloses a technique of synthesizing the metal fine particles by using metal salts such as nitrate salt, sulfate salt, carbonate, and chloride, as metal sources.    Patent document 1: Japanese Patent Laid Open Publication No. 2005-177983    Patent document 2: Japanese Patent Laid Open Publication No. 2005-211730    Patent document 3: Patent Publication No. 2561537    Patent document 4: Japanese Patent Laid Open Publication No. 2007-31835    Patent document 5: Japanese Patent Laid Open Publication No. 2007-63580    Patent document 6: Japanese Patent Laid Open Publication No. 2006-307341
However, the production of the metal fine particles by the aforementioned physical method has a problem that a large apparatus such as a vacuum chamber is used involving a high cost with low throughput, thus requiring an extremely high production cost.
Further, the production of the metal fine particles by the aforementioned chemical method has a problem that an environmental load is great as the producing method, because of a high cost of a raw material and because lots of raw materials are toxic materials. Specifically, in the producing method disclosed in the patent documents 4 and 5, although the organic metal compound such as a metal carbonyl compound is used as a raw material, lots of organic metal compounds are toxic materials and expensive. Further, in the producing method disclosed in the patent document 6, although the metal salt is used as the raw material, metal salts such as nitrate salt, sulfate salt, carbonate, and chloride are also toxic materials, and anions (nitrate ion, sulfate ion, carbonate ion, and chloride ion, etc.,), which are derived from a raw material, is remained in a solution after producing the fine particles, thus requiring a step of desalting is required. Further, in order to produce fine particles with uniform particle sizes, such fine particles need to be produced by a diluted solution, thus requiring a large quantity of solvent and accordingly requiring a treatment to a large quantity of waste liquid.